[Elecraft] KPA 500 6meter power out.

[Mike Streeter]

I have had this problem for some time but as I almost never use 6 meters it has not really concerned me.
I have two identical K Line stations, K3's, KAT 500's, KPA 500's and P3's.
On station #1 everything works as it should and if I put 25 watts into the KPA 500 I get 500+ watts out. On station #2 if I put 30 watts into the KPA 500 I get 350 out and if I increase the input to 32 watts the KPA 500 momentarily shows 400 watts out and immediately trips the amp and shows the PA DISS fault. It works fine on all other bands putting out 500 watts with nominal drive power.
If I then swop the KPA 500's over without changing any antennas or radio settings (so nothing except the amps has changed), the fault moves with the amp and the good amp continues to be good on the other station.
My questions: What is wrong with the faulty amp and what do I need to do to fix it?
Many thanks for reading.
Mike, WM5DX.